Push-pull transducer

ABSTRACT

An electro-acoustic transducer is disclosed comprising an enclosing hollow piston element of relatively light rigid nonmagnetic material; a central vibratory mass element is situated within said piston element having opposite portions of magnetic material. The use of the piston-action vibrator unit eliminates complex modes of vibration, resulting in higher efficiency than ordinary diaphragm action.

Unite States 1191 Chervenals Apr. 3, 1973 .mw nm 3 HC [54] PUSH-PULLTRANSDUCER 2,413,012 12/1946 2,713,127 7/1955 [75] Inventor.JohnChervenak,Wash1ngton,D.C. 2,723,386 "955 The United States ofAmerica as [73] Assignee:

represented b th secretary f th Primary ExaminerR0dney D. Bennett, Jr. NAssistant Examiner-D, M. Potenza Attorney-R. S. Sciascia, A. L. Branningand M. 1. Crane [22] Filed: Sept. 24, 1956 [57] ABSTRACT Anelectro-acoustic transducer is disclosed comprising 21 Appl. No.:611,798

an enclosing hollow piston element of relatively light rigid nonmagneticmaterial; a central vibratory mass element is situated within saidpiston element having opposite portions of magnetic material. The use ofthe piston -action vibrator unit eliminates complex modes ation,resulting in higher efficiency than ordinary diaphragm action.

References Cited UNITED STATES PATENTS of vibr 12 Claims, 7 DrawingFigures 1,640,538 DuBois-Reymond ....................340/8 2,025,041Colton............ ....340/8 PATENTEUAPR3 I975 SHEET 1 UP 3' VENTOR ENAKJO H N. CH ERV Pmimmm m5 3,725,856

sumaors INVE. JOHN CHERVEN BY Z L,

W ATTORNEY) PUSH-PULL TRANSDUCER The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

The present invention relates in general to underwater electro-acoustictransducers and has particular reference to such a transducer forprojection and reception of underwater low-frequency compressionalwaves.

An object of the invention is the provision of a piston-action vibratorunit in which complex modes of vibration, as in the case of a diaphragm,are avoided and a substantially true piston action is attained resultingin higher efficiency than realizable from ordinary diaphragm action ofan energy radiating face. The term piston action indicates such actionas the movement of a substantially flat surface element such that allparts on the surface element oscillate in synchronism, normal to thesurface and with the same amplitude.

Another object of the invention is the attainment of a high radiatingpower at low frequencies in the neighborhood of l kilocycle with simpleand sturdy apparatus in the form of independently operable units capableof being used in various multi-unit arrays.

A further object is the provision of a vibrator unit having a pistonaction and operable to vibrate bodily as a unit and only along the axisof the piston surface, and readily adaptable to combination with anynumber of light units in various compact arrays for operation insynchronism as a single large piston or in any desired phase relation.

Various other objects and advantages of the invention will becomeapparent upon a perusal of the following specification and the drawingsaccompanying the same.

In the Drawings:

FIG. 1 is a partially expanded view in autographic projection of apreferred embodiment of the invention.

FIG. 2 is a section on the line 22 of FIG. 3

FIG. 3 is a staggered section on the line3-3 of FIG. 2.

FIG. 4 is a side view of a complete unit with the waterproof coveringand sponge rubber backing in section.

FIG. 5 is a front view of an array of four of the units.

FIG. 6 is a schematic circuit diagram of a unit.

FIG. 7 is a fragmentary sectional view of a modification.

Referring to the drawings in detail, the partially expanded view of FIG.1 shows the various parts in their proper cooperative relation exceptthat the rear wall 10, here shown on top, together with the magneticinwardly facing element 11 carried thereby is moved away from theremainder of the assemblage to show lower adjacent parts otherwiseobscured. With all parts in their proper relative position as shown inFIGS. 2 and 3, the magnetic elements 11 and 12 are positioned in closeproximity through a suitable narrow working air gap 13.

The hollow piston element designated as a whole by the reference numeral14 is formed of the six walls l0, l5, l6, 17, 18 and 19, of relativelylight, rigid, nonmagnetic material such as aluminum, the walls andforming ,the rear and front end walls of the bodily vibratingpiston-action unit. In the present embodiment the walls are secured inassembled relation by screws as indicated at 20 (FIG. 1) threaded intothreaded bores such as 21 in an abutting wall element and bondedtogether for rigidity and watertightness by a suitable cement suchasEpox and epoxy cement, not shown.

A central vibrating mass element consisting of a center slab 22preferably of aluminum or other nonmagnetic material with opposite sideportions 12, 23 (FIG. 2) of low reluctance magnetic material secured tothe plate 22 through intermediate mass elements 24, 25, is supportedwithin the hollow piston element free of the side walls l6, l7, l8 and19, by a spring coupling to the opposite end walls 10, 15, which formthe endsof the hollow piston, through spring elements 26. The side wallsand piston ends thus have freedom of movement as a unit independently ofthe central vibratory mass. This coupling to the end walls 10 and 15 ofthe piston is effected through spring assemblies each consisting of arow of three ring-shaped springs 26 secured between a pair of mountingbars such as the bars 27 and 28. As shown in FIGS. 1 and 2, the springelements 26 connect the central element to opposite end walls of thepiston element in the direction of relative movement between thecentral'element and the piston .element and independently of the sidewalls. The bars 27 are rigidly bonded to one side of the center plate 22along a marginal edge in any known or other suitable manner as bybrazing, welding or bonding with a suitable cement such as an epoxycement, the latter being used in the present instance. To insure properalignment and facilitate the bonding, use is made of bolts 29. (FIG. 1passing through the center plate to similarly secure the barv 27 ofanother spring assembly on the opposite side of the plate. The bars 28of the spring assemblies are also rigidly .bonded to the inner side ofan adjacent end wall 10 or 15 near the outer marginal edges of the endwalls. In the present instance the spring rings 26 are secured to thebars by brazing, the rings being fitted into complementary curvednotches 31 (FIG. 1) in the bars to provide substantial brazing surfacebetween the ring and bar.

The low reluctance magnetic elements 12 and 23 carried by the centerplate 22 are laminated as indicated for element 12 in FIGS. 1 and 3, andrigidly secured to adjacent intermediate slabs 24, 25 by a suitablecement such as an epoxy cement, while the slabs 24, 25 are similarlyrigidly secured to the center plate 22. The intermediate slabs 24, 25are of metal which may be nonmagnetic or magnetic inasmuch as their mainfunction is to add mass and desired thickness to the central vibratorymass element comprised of the elements 22, 24, 25, 12 and 23. Whereexpedient, the low reluctance magnetic elements 12 and 23 may be made ofsufficient depth to take on the function of the elements 24 and 25, ofsupplying mass and spacing.

Laminated electro-magnet elements 11 and 32 are rigidly secured to theinner sides of the rear and front end walls 10 and 15 respectively toform in effect substantially rigid end walls having a portion formed oflow reluctance material for cooperation with the'magnet elements 12 and23. Energization of these low reluctance portions or elements 11 and 32is effected by suitable energizing coil elements 33 and 34 potted inplastic and formed to fit into E-slots in the outer laminated magnetelements 11, 32, there being three such potted coils for each of theelectro-magnetic elements ll, 32. Thus when the coils are energizedthere will be induced a magnetic flux confined substantially to pairs ofadjacent magnetic elements such as 11, 12 and the air gap 13 betweenthem as indicated by the flux path arrows 35 in FIG. 2, with consequentvariation in attractive force between the complementary magneticelements in proportion to variations in current flow through the coils.Current leads 36 (FIGS. 1 and 3) for the coils are continued out fromthe piston element through the back end wall via a suitable water-tightstuffing box 37 and cable 38 (FIG. 1).

To complete the unit for use under water in an array of a plurality ofsuch units, it is provided as indicated in FIG. 4 with a protectivewater-tight coating 39 of noncorrosive material such as neoprene orother suitable material and backed at the rear end wall with a soundabsorbing pad 40 of any known or other suitable material such asair-cell rubber to prevent substantial back radiation or reception bythe vibratory piston unit. For use in an array, any number of units maybe placed in a suitable frame as in FIG. 5 where an arrangement for afour unit array is shown. Here the frame 41 comprises four cells withopen fronts into which the units 14 are nested and held in place byretaining cleats 42 backed with a sheet rubber pad 43 and bolted on atthe corners of the cells. These rubber pads function to allow themaximum displacement of the piston units required for the particularuse. For example, in one particular use for underwater soundtransmission and reception the displacement may be of the order oftwo-thousandths of an inch.

In use each piston unit is connected in a circuit as shown in theschematic diagram of FIG. 6. Here the two multiple groups, oneconsisting of the three rear coils 33 connected in multiple, and theother the three front coils 34 connected in multiple, are connected inseries across a direct current source B of polarizing current such as abattery, over a circuit which may be traced from the battery B throughcoils 33 in parallel, coils 34 in parallel and back to battery B. Forsignal current each group of coils is connected in parallel through ablocking condenser 44 and 45 with a source 46 of alternating signalcurrent. To obtain good linearity and maximum power the circuit isarranged to so direct the biasing and signal currents through the coilsas to operate the unit in push-pull and in a manner which requires nochokes in the direct current polarizing circuit. This is accomplished bydirecting the polarizing current flow from the battery through the coilsin a given direction in series through the two groups and the signalcurrent through the two groups in parallel thus aiding the polarizingcurrent in one group and reducing it in the other according to thedirection of the signal current. The polarization being of sufficientstrength as not to be reduced to zero by opposing cycles in the signalcurrent, opposite variations in the attraction between opposite sides ofthe central element and the adjacent ends of the enclosing pistonelement will take place in a push-pull effect to produce correspondingvibration of the piston element as a unit. While the above operation hasbeen described as applied to a single unit it will be understood thatall or any number of the units in an array may be so operated inphase orin any phase relation desired, and that both projection and reception ofcompressional waves is substantially unidirectional due to theabsorption pads on the rear end walls of the unit.

It will be noted that with the central vibratory element mounted withinthe hollow piston element free of the side walls and connected only tothe peripheral margins of the substantially rigid end walls, the endwalls are caused to vibrate bodily in true piston action withoutbreaking up into out-of-phase vibrations or vibrations of differentamplitude, as in the case of a vibrating diaphragm. Thus due to themounting of the central vibratory element free of the side walls, thereis no lateral movement of the side walls and substantially all parts ofthe piston element vibrate only along the axis X-X, FIG. 1.

In the modification of FIG. 7, the nonmagnetic elastic means connectingthe movable elements takes the form of a sheet 47 of elastic,nonmagnetic, nonconducting material such as rubber, filling the gapbetween the complementary magnetic elements 11 and 12.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. An electro-acoustic transducer comprising an enclosing hollow pistonelement of relatively light rigid nonmagnetic material havingsubstantially rigid side walls and a pair of parallel oppositesubstantially flat rigid end walls, a central vibratory mass elementsituated within said piston element having opposite portions of magneticmaterial, said end walls of the piston element having portions ofmagnetic material spaced from adjacent said portions of the central masselement by an air gap, spring means of heavy duty spring material, ascompared with said portions of magnetic material, directly connectingsaid central mass element and end walls independently of the side wallsfor transmitting motion directly between the vibrating mass and the endwalls, and means for inducing a magnetic flux in said portions ofmagnetic material, whereby flux paths through magnetic material in shuntof the air gap are avoided.

2. An electro-acoustic transducer comprising a vibratory central masselement having opposite outwardly facing side portions of magneticmaterial, an enclosing substantially rigid freely movable hollow pistonelement having substantially rigid end walls with inwardly facingportions of magnetic material separated from adjacent outwardlyfacingsides of the central element by air gaps and side walls of substantiallyrigid nonmagnetic material, spring means directly connecting saidcentral mass element with the said end walls, and means for inducing amagnetic flux in the said outwardly facing side portions of the centralelement and said inwardly facing portions of the end walls whereby theinduced flux is confined substantially to the said gages independentlyof the side walls.

3. An electro-acoustic transducer comprising a central vibratory masselement, an enclosing piston element of nonmagnetic material havingsubstantially rigid side walls and parallel opposite end walls, twoopposite sides of said central element facing the end walls havingportions of magnetic material, said end walls of the piston elementbeing adjacent to said opposite sides of said central element and havingportions of magnetic material separated by an air gap from the saidportions of the central element, means for inducing a magnetic fluxthrough said portions of magnetic material and air gap, and spring meansdirectly connecting said magnetic portions of said central element andthe piston element through nonmagnetic material independently of saidside walls, all portions of said piston element except said magneticportions of the end walls being of nonmagnetic material, whereby thepaths of lowest reluctance of said induced flux is limited to said airgap and said portions of magnetic material.

4. An electro-acoustic transducer comprising a central vibratory masselement having a portion of magnetic material, a hollow piston elementof nonmagnetic material enclosing said central element and having aportion of one end wall formed of magnetic material spaced from thecentral element by an air gap, means for inducing a magnetic fluxthrough said portions of magnetic material and air gap, and meansresiliently connecting said portions around the air gap throughnonmagnetic material, whereby the path of lowest reluctance for saidinduced flux is confined mainly to said portions of magnetic materialand said air gap, independently of said connecting means and pistonelement.

5. An electro-acoustic transducer comprising a pair of separaterelatively movable vibratory mass elements one within the other, theouter mass element being in the form of a hollow piston having rigidside walls of nonmagnetic material and a pair of rigid end walls ofnonmagnetic material, a pair of complementary magnetic elements carriedone on each of a pair of adjacent portions of said mass elements andspaced by an air gap, and compression spring means connecting said innermass element directly with the end walls independently of the sidewalls.

6. An electro-acoustic transducer comprising a rigid hollow pistonelement of nonmagnetic material having substantially rigid side wallsand a pair of opposite parallel end walls, an inner platform element ofnonmagnetic material situated centrally within the hollow piston spacedfrom the side walls thereof and parallel to said end walls, pairs ofcomplementary magnetic elements fixed respectively to the inside of eachof said pair of end walls and adjacent side wall of said platform withan air gap between said magnetic elements, means for inducing a magneticflux through said magnetic elements and said air gap, and spring meansdirectly connecting said platform with the peripheral margin of theinner side of the end walls independently of the side walls, said pairsof complementary elements being magnetically separated from each otherby the nonmagnetic material of the inner platform and piston, wherebythe induced magnetic flux is confined to a passage through the magneticelements and the intervening air gap.

7. An electro-acoustic transducer comprising a substantially rigidcubicle hollow piston element having side walls and a pair of end wallsof nonmagnetic material, a relatively movable inner vibratory masselement of nonmagnetic material wholly disconnected from the inner sidesof the piston element, spring means directly connecting the peripheralmargin of said inner element and the peripheral margins of said twoopposite end walls of said piston element for transmission of pressurevariations from said inner element to said opposite end wallsindependently of the side walls, mass elements of magnetic materialcarried on opposite sides of said inner elements, other mass elements ofmagnetic material one carried by each of said opposite end walls andspaced from the adjacent inner mass element by an air gap, and means forinducing a magnetic flux through a pair of adjacent said mass elementsand the intervening air gap.

8. An electro-acoustic transducer comprising a pair of separaterelatively movable vibratory mass elements one within the other, a pairof complementary magnetic elements carried one on each of a pair ofadjacent sides of said mass elements and spaced by a gap to permitrelative movement between them, and spring means connecting saidrelatively movable elements through nonmagnetic material interposedbetween said complementary magnetic elements, whereby a shunting ofmagnetic flux through the connection between the relatively movableelements is prevented.

9. An electro-acoustic transducer comprising a pair of separaterelatively movable vibratory mass elements one within the other, a pairof complementary magnetic elements carried one on each of a pair ofadjacent sides of said mass elements and spaced by a gap to permitrelative movement between them, and nonmagnetic elastic means interposeddirectly between and connecting said complimentary magnetic elements.

10. The improvement of an electro-acoustic transducer comprising asealed housing formed of a tubular body having an end plate at each endthereof, a center plate having a pair of axially opposed faces,resilient means suspending said center plate for axial movement betweensaid end plates, a first electromagnetic assembly having a portionmounted on one end plate and a portion mounted on one face of saidcenter plate, a second electromagnetic assembly having a portion mountedon the other end plate and a portion mounted on the other face of saidcenter plate, magnetizing coil means associated with each one of saidelectromagnetic assemblies, sealed electrical terminal means in saidhousing connected to each magnetizing coil means for enabling electricalconnection to be established through said housing to said magnetizingcoil means.

11. In an electro-acoustic transducer the combination comprising a baseplate having a pair of opposite parallel plane surfaces, a first set ofmagnetic armature assemblies securely bonded to each of said planesurfaces, each of said armature assemblies having its unbonded surfacepositioned in a plane parallel to the surface of said base plate, asealed housing structure totally enclosing said base and armatureassemblies, said housing structure having a pair of opposite end plates,a second set of magnetic armature assemblies bonded to the innersurfaces of said opposite end plates, the unbonded surfaces of saidsecond set of magnetic armature assemblies lying in parallel planes andpositioned closely adjacent to the plane surfaces of said first set ofmagnetic armature assemblies, spring spacer means attached between theopposite plane surfaces of said base plate and the inner surfaces ofsaid opposite end plates of said housing structure, magnetizing coilmeans associated with each set of magnetic areach of said magneticmeans, connection means for supplying electrical current to said currentcoil, and spring elements attached between said first and secondmagnetic means to hold said magnetic means in operable relationship toeach other whereby translatory vibration of the housing structure willresult in opposite phase to the translatory vibration of said firstmagnetic means whenever alternating current is supplied to the currentcoils.

1. An electro-acoustic transducer comprising an enclosing hollow pistonelement of relatively light rigid nonmagnetic material havingsubstantially rigid side walls and a pair of parallel oppositesubstantially flat rigid end walls, a central vibratory mass elementsituated within said piston element having opposite portions of magneticmaterial, said end walls of the piston element having portions ofmagnetic material spaced from adjacent said portions of the central masselement by an air gap, spring means of heavy duty spring material, ascompared with said portions of magnetic material, directly connectingsaid central mass element and end walls independently of the side wallsfor transmitting motion directly between the vibrating mass and the endwalls, and means for inducing a magnetic flux in said portions ofmagnetic material, whereby flux paths through magnetic material in shuntof the air gap are avoided.
 2. An electro-acoustic transducer comprisinga vibratory central mass element having opposite outwardly facing sideportions of magnetic material, an enclosing substantially rigid freelymovable hollow piston element having substantially rigid end walls withinwardly facing portions of magnetic material separated from adjacentoutwardly facing sides of the central element by air gaps and side wallsof substantially rigid nonmagnetic material, spring means directlyconnecting said central mass element with the said end walls, and meansfor inducing a magnetic flux in the said outwardly facing side portionsof the central element and said inwardly facing portions of the endwalls whereby the induced flux is confined substantially to the saidgages independently of the side walls.
 3. An electro-acoustic transducercomprising a central vibratory mass element, an enclosing piston elementof nonmagnetic material having substantially rigid side walls andparallel opposite end walls, two opposite sides of said central elementfacing the end walls having portions of magnetic material, said endwalls of the piston element being adjacent to said opposite sides ofsaid central element and having portions of magnetic material separatedby an air gap from the said portions of the central element, means forinducing a magnetic flux through said portions of magnetic material andair gap, and spring means directly connecting said magnetic portions ofsaid central element and the piston element through nonmagnetic materialindependently of said side walls, all portions of said piston elementexcept said magnetic portions of the end walls being of nonmagneticmaterial, whereby the paths of lowest reluctance of said induced flux islimited to said air gap and said portions of magnetic material.
 4. Anelectro-acoustic transducer comprising a central vibratory mass elementhaving a portion of magnetic material, a hollow piston element ofnonmagnetic material enclosing said central element and having a portionof one end wall formed of magnetic material spaced from the centralelement by an air gap, means for inducing a magnetic flux through saidportions of magnetic material and air gap, and means resilientlyconnecting said portions around the air gap through nonmagneticmaterial, whereby the path of lowest reluctance for said induced flux isconfined mainly to said portions of magnetic material and said air gap,independently of said connecting means and piston element.
 5. Anelectro-acoustic transducer comprising a pair of separate relativelymovable vibratory mass elements one within the other, the outer masselement being in the form of a hollow piston havIng rigid side walls ofnonmagnetic material and a pair of rigid end walls of nonmagneticmaterial, a pair of complementary magnetic elements carried one on eachof a pair of adjacent portions of said mass elements and spaced by anair gap, and compression spring means connecting said inner mass elementdirectly with the end walls independently of the side walls.
 6. Anelectro-acoustic transducer comprising a rigid hollow piston element ofnonmagnetic material having substantially rigid side walls and a pair ofopposite parallel end walls, an inner platform element of nonmagneticmaterial situated centrally within the hollow piston spaced from theside walls thereof and parallel to said end walls, pairs ofcomplementary magnetic elements fixed respectively to the inside of eachof said pair of end walls and adjacent side wall of said platform withan air gap between said magnetic elements, means for inducing a magneticflux through said magnetic elements and said air gap, and spring meansdirectly connecting said platform with the peripheral margin of theinner side of the end walls independently of the side walls, said pairsof complementary elements being magnetically separated from each otherby the nonmagnetic material of the inner platform and piston, wherebythe induced magnetic flux is confined to a passage through the magneticelements and the intervening air gap.
 7. An electro-acoustic transducercomprising a substantially rigid cubicle hollow piston element havingside walls and a pair of end walls of nonmagnetic material, a relativelymovable inner vibratory mass element of nonmagnetic material whollydisconnected from the inner sides of the piston element, spring meansdirectly connecting the peripheral margin of said inner element and theperipheral margins of said two opposite end walls of said piston elementfor transmission of pressure variations from said inner element to saidopposite end walls independently of the side walls, mass elements ofmagnetic material carried on opposite sides of said inner elements,other mass elements of magnetic material one carried by each of saidopposite end walls and spaced from the adjacent inner mass element by anair gap, and means for inducing a magnetic flux through a pair ofadjacent said mass elements and the intervening air gap.
 8. Anelectro-acoustic transducer comprising a pair of separate relativelymovable vibratory mass elements one within the other, a pair ofcomplementary magnetic elements carried one on each of a pair ofadjacent sides of said mass elements and spaced by a gap to permitrelative movement between them, and spring means connecting saidrelatively movable elements through nonmagnetic material interposedbetween said complementary magnetic elements, whereby a shunting ofmagnetic flux through the connection between the relatively movableelements is prevented.
 9. An electro-acoustic transducer comprising apair of separate relatively movable vibratory mass elements one withinthe other, a pair of complementary magnetic elements carried one on eachof a pair of adjacent sides of said mass elements and spaced by a gap topermit relative movement between them, and nonmagnetic elastic meansinterposed directly between and connecting said complimentary magneticelements.
 10. The improvement of an electro-acoustic transducercomprising a sealed housing formed of a tubular body having an end plateat each end thereof, a center plate having a pair of axially opposedfaces, resilient means suspending said center plate for axial movementbetween said end plates, a first electromagnetic assembly having aportion mounted on one end plate and a portion mounted on one face ofsaid center plate, a second electromagnetic assembly having a portionmounted on the other end plate and a portion mounted on the other faceof said center plate, magnetizing coil means associated with each one ofsaid electromagnetic assemblies, sealed electrical terminal means insaid housing connected to each magnetizinG coil means for enablingelectrical connection to be established through said housing to saidmagnetizing coil means.
 11. In an electro-acoustic transducer thecombination comprising a base plate having a pair of opposite parallelplane surfaces, a first set of magnetic armature assemblies securelybonded to each of said plane surfaces, each of said armature assemblieshaving its unbonded surface positioned in a plane parallel to thesurface of said base plate, a sealed housing structure totally enclosingsaid base and armature assemblies, said housing structure having a pairof opposite end plates, a second set of magnetic armature assembliesbonded to the inner surfaces of said opposite end plates, the unbondedsurfaces of said second set of magnetic armature assemblies lying inparallel planes and positioned closely adjacent to the plane surfaces ofsaid first set of magnetic armature assemblies, spring spacer meansattached between the opposite plane surfaces of said base plate and theinner surfaces of said opposite end plates of said housing structure,magnetizing coil means associated with each set of magnetic armatureassemblies, sealed electrical terminal means connected to saidmagnetizing coil means and adapted to permit electrical connection to beestablished through the housing structure to the magnetizing coil means.12. An electromagnetic transducer comprising a sealed housing structurehaving positioned therewithin first magnetic means mounted fortranslatory vibration, second magnetic means attached to said housingstructure and located in operable relationship to said first magneticmeans, current coil means associated with each of said magnetic means,connection means for supplying electrical current to said current coil,and spring elements attached between said first and second magneticmeans to hold said magnetic means in operable relationship to each otherwhereby translatory vibration of the housing structure will result inopposite phase to the translatory vibration of said first magnetic meanswhenever alternating current is supplied to the current coils.